Gap SANS-201: Determine if altered atmospheric conditions (e.g., elevated ambient CO2, mild hypoxia from exploration atmosphere) has a contributing role in the development of ocular manifestations.
Last Published:  03/26/21 03:33:57 PM (Central)
Responsible Element: Human Health Countermeasures (HHC)
Status: Open
Description
Present state of knowledge: Carbon dioxide levels are mildly elevated on ISS and could lead to vasodilation and/or changes in pH levels in the body during spaceflight, and thereby increase the headward fluid shift and/or ICP. Evidence to date does not support a major role for CO2 in SANS pathophysiology, given that optic disc edema continues to develop in astronauts despite lowering of CO2 levels on the ISS, and the observation that bed rest subjects exposed to strict head-down tilt bed rest without elevated levels of CO2 also developed SANS-like manifestations. Also of note, in another bedrest study that involved strict head-down tilt bed rest where ambient CO2 was elevated to 4 mmHg, while SANS manifestations developed, the elevated CO2 during bed rest did not cause increases in arterial CO2 levels of the subjects, or other physiological adaptations, indicating the mild elevation in CO2 did not have a physiologic effect. Future space vehicles and/or habitats may additionally use an altered atmosphere that is hypobaric, has a hyperoxic gas mixture (34% oxygen at a pressure of 8.2psi, which equates to an approximate earth altitude of 4000 ft), and overall results in mild hypobaric hypoxia. This atmosphere will reduce the time needed for astronauts to conduct pre-breathe protocols before extravehicular activities (EVAs). Because hypobaric hypoxia is known to cause high altitude cerebral edema (HACE) there is some concern that exposure to hypobaric hypoxia in crewmembers who have developed SANS may exacerbate or worsen their SANS manifestations.

Research approach: HRP will fund studies via solicited and directed mechanisms as deemed necessary. Examples of types of studies that may be conducted include but are not limited to: Further head-down tilt or flight studies to quantify a dose-response curve of effects of combined elevated CO2 with fluid shifts. The combination of head-down tilt bed rest with exposure to the hypobaric/hypoxic exploration atmosphere, and the effects of this combined exposure on SANS outcomes is another planned area of research.
Target for Closure
Quantification of the effects of combined exposures: headward fluid-shifts in combination with elevated CO2, and headward fluid-shifts plus added mild hypobaric hypoxia. Note: The HFBP Element is conducting similar evaluations with regards to brain/cognitive/sleep changes.
Mappings
Risk Risk of Spaceflight Associated Neuro-ocular Syndrome (SANS)
You are here! Gap SANS-201: Determine if altered atmospheric conditions (e.g., elevated ambient CO2, mild hypoxia from exploration atmosphere) has a contributing role in the development of ocular manifestations.
Completed
Planned-Funded
Terminated

Documentation:
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